First report of <italic>Cytauxzoon</italic> sp. infection in domestic cats in Switzerland: natural and transfusion-transmitted infections.

Background: Cytauxzoonosis is an emerging tick-borne disease of domestic and wild felids. <italic>Cytauxzoon felis</italic> induces severe and often fatal disease in domestic cats. In Europe, clinical and subclinical infections caused by <italic>Cytauxzoon</italic> sp. are described. We report the first cases of <italic>Cytauxzoon</italic> sp. infection in domestic cats in Switzerland. Methods: Clinical and laboratory data and results of PCR analyses were collected from <italic>Cytauxzoon</italic> sp. PCR-positive cats and the cats followed for up to 851 days. Results: The cases were three two-month old kittens from the same litter (Cases 1–3) and two adult domestic shorthair cats (Cases 4 and 5). The cats originated from the north-west and west of Switzerland. Cases 1–3 presented with moderate to severe regenerative anaemia and intraerythrocytic inclusions. <italic>Cytauxzoon</italic> sp<italic>.</italic> was confirmed by PCR and sequencing<italic>.</italic> The kittens made a clinical and haematological recovery after blood transfusion and/or treatment with azithromycin and atovaquone, but erythroparasitaemia persisted. Case 4 presented with severe non-regenerative anaemia. Case 5 was healthy and used as a blood donor for Case 4. Following blood transfusion, Case 4 showed intraerythrocytic inclusions, and <italic>Cytauxzoon</italic> sp<italic>.</italic> was confirmed in both Cases 4 and 5 using PCR and sequencing. Case 4 achieved clinical and haematological remission after treatment with azithromycin, atovaquone and immunosuppressive drugs. Eight months later, Case 4 was presented again with anaemia but tested <italic>Cytauxzoon</italic> sp. PCR-negative. Sequencing of 1637 bp of the <italic>18S</italic> rRNA gene of <italic>Cytauxzoon</italic> sp<italic>.</italic> revealed 100% nucleotide sequence identity among isolates of Cases 1–3 and between isolates of Cases 4 and 5, and 99% sequence identity between isolates of all cases. Phylogenetic analysis revealed the closest relationship of the Swiss isolates to <italic>Cytauxzoon</italic> sp<italic>.</italic> isolates from domestic cats and wild felids from France, Spain and Romania and to <italic>Cytauxzoon manul</italic> from a Pallas's cat. Conclusions: This is the first report of <italic>Cytauxzoon</italic> sp<italic>.</italic> infection in domestic cats in Switzerland. It is also the first report of infection in very young kittens and transmission of <italic>Cytauxzoon</italic> sp<italic>.</italic> to an adult cat by transfusion of blood from an asymptomatic cat. The cats recovered but some developed chronic asymptomatic erythroparasitaemia for up to 28 months. Domestic cats may act as reservoirs for <italic>Cytauxzoon</italic> sp. in Europe and blood donor cats should be screened for this agent by PCR. [ABSTRACT FROM AUTHOR]